diff --git a/frontend/src/App.jsx b/frontend/src/App.jsx
index 951ebf7..b545339 100644
--- a/frontend/src/App.jsx
+++ b/frontend/src/App.jsx
@@ -31,6 +31,7 @@ import AdminMaturityModelsPage from './pages/AdminMaturityModelsPage'
 import TrainerContextsPage from './pages/TrainerContextsPage'
 import MediaWikiImportPage from './pages/MediaWikiImportPage'
 import AdminUsersPage from './pages/AdminUsersPage'
+import ActiveClubSwitcher from './components/ActiveClubSwitcher'
 import './app.css'
 
 // Bottom Navigation (Mobile)
@@ -99,8 +100,11 @@ function ProtectedLayout() {
       <DesktopSidebar isAdmin={isAdmin} user={user} onLogout={handleLogout} />
       <div className="app-shell">
         <div className="app-shell__column">
-          <div className="app-header app-header--mobile">
-            <div className="app-logo">🥋 Shinkan</div>
+          <div className="app-header app-header--mobile app-header--mobile-stack">
+            <div className="app-header-mobile__top">
+              <div className="app-logo">🥋 Shinkan</div>
+            </div>
+            <ActiveClubSwitcher variant="mobile" />
           </div>
           <div className="app-main">
             <Outlet />
diff --git a/frontend/src/app.css b/frontend/src/app.css
index 9868097..4ebd9a0 100644
--- a/frontend/src/app.css
+++ b/frontend/src/app.css
@@ -69,8 +69,42 @@ body { font-family: var(--font); background: var(--bg); color: var(--text1); -we
     padding-right: max(16px, env(safe-area-inset-right, 0px));
   }
 }
+.app-header--mobile-stack {
+  flex-direction: column;
+  align-items: stretch;
+  gap: 0.5rem;
+  padding-bottom: 10px;
+}
+.app-header-mobile__top {
+  display: flex;
+  align-items: center;
+  min-height: var(--header-h);
+}
 .app-logo { font-size: 18px; font-weight: 700; color: var(--accent); letter-spacing: -0.02em; }
 
+.active-club-switch {
+  display: flex;
+  flex-direction: column;
+  gap: 0.35rem;
+}
+.active-club-switch__label {
+  font-size: 0.75rem;
+  font-weight: 500;
+  color: var(--text2);
+}
+.active-club-switch__select {
+  width: 100%;
+  font-size: 0.875rem;
+  padding: 0.4rem 0.5rem;
+}
+.active-club-switch--sidebar {
+  width: 100%;
+  padding-bottom: 4px;
+}
+.active-club-switch--mobile {
+  width: 100%;
+}
+
 /* === Seiten-Inhalt: volle Breite der Spalte, kein künstlicher Max-Wert auf großen Screens === */
 .app-page {
   width: 100%;
@@ -2198,7 +2232,14 @@ a.analysis-split__nav-item {
 
 .desktop-sidebar__footer {
   border-top: 1px solid var(--border);
-  padding: 16px 12px 0;
+  padding: 16px 12px 16px;
+  display: flex;
+  flex-direction: column;
+  align-items: stretch;
+  gap: 12px;
+}
+
+.desktop-sidebar__footer-row {
   display: flex;
   align-items: center;
   gap: 8px;
diff --git a/frontend/src/components/ActiveClubSwitcher.jsx b/frontend/src/components/ActiveClubSwitcher.jsx
new file mode 100644
index 0000000..0243b79
--- /dev/null
+++ b/frontend/src/components/ActiveClubSwitcher.jsx
@@ -0,0 +1,44 @@
+import { useAuth } from '../context/AuthContext'
+
+/**
+ * Zeigt einen Vereins-Umschalter, wenn der Nutzer mehreren Vereinen zugeordnet ist.
+ * Steuert den Mandanten-Kontext (Header X-Active-Club-Id + Profilfeld active_club_id).
+ */
+export default function ActiveClubSwitcher({ variant = 'sidebar' }) {
+  const { user, setActiveClub } = useAuth()
+  const clubs = user?.clubs || []
+  if (clubs.length <= 1) return null
+
+  const selectClubId =
+    user?.active_club_id != null && clubs.some((c) => c.id === user.active_club_id)
+      ? user.active_club_id
+      : clubs[0]?.id
+
+  const isMobile = variant === 'mobile'
+
+  return (
+    <label
+      className={
+        'active-club-switch' +
+        (isMobile ? ' active-club-switch--mobile' : ' active-club-switch--sidebar')
+      }
+    >
+      <span className="active-club-switch__label">Aktiver Verein</span>
+      <select
+        className="form-input active-club-switch__select"
+        aria-label="Aktiven Verein wählen"
+        value={selectClubId ?? ''}
+        onChange={(e) => {
+          const v = e.target.value
+          if (v) setActiveClub(Number(v))
+        }}
+      >
+        {clubs.map((c) => (
+          <option key={c.id} value={c.id}>
+            {c.name || `Verein #${c.id}`}
+          </option>
+        ))}
+      </select>
+    </label>
+  )
+}
diff --git a/frontend/src/components/DesktopSidebar.jsx b/frontend/src/components/DesktopSidebar.jsx
index b95be31..a918e17 100644
--- a/frontend/src/components/DesktopSidebar.jsx
+++ b/frontend/src/components/DesktopSidebar.jsx
@@ -1,6 +1,7 @@
 import { NavLink, useLocation } from 'react-router-dom'
 import { LogOut } from 'lucide-react'
 import { getMainNavItems } from '../config/appNav'
+import ActiveClubSwitcher from './ActiveClubSwitcher'
 
 function sidebarLinkActive(pathname, item, routerIsActive) {
   if (item.to.startsWith('/admin')) return pathname.startsWith('/admin')
@@ -46,40 +47,43 @@ export default function DesktopSidebar({
       </nav>
 
       <div className="desktop-sidebar__footer">
-        <div className="desktop-sidebar__user">
-          <div
-            style={{
-              width: 32,
-              height: 32,
-              borderRadius: '50%',
-              background: 'var(--accent)',
-              display: 'flex',
-              alignItems: 'center',
-              justifyContent: 'center',
-              color: 'white',
-              fontWeight: 600,
-              fontSize: '14px'
-            }}
+        <ActiveClubSwitcher variant="sidebar" />
+        <div className="desktop-sidebar__footer-row">
+          <div className="desktop-sidebar__user">
+            <div
+              style={{
+                width: 32,
+                height: 32,
+                borderRadius: '50%',
+                background: 'var(--accent)',
+                display: 'flex',
+                alignItems: 'center',
+                justifyContent: 'center',
+                color: 'white',
+                fontWeight: 600,
+                fontSize: '14px'
+              }}
+            >
+              {(user?.name || user?.email || '?').trim().slice(0, 1).toUpperCase()}
+            </div>
+            <div className="desktop-sidebar__user-text">
+              <span className="desktop-sidebar__user-name">
+                {user?.name || user?.email || 'User'}
+              </span>
+              {tier ? (
+                <span className="desktop-sidebar__user-tier">{tier}</span>
+              ) : null}
+            </div>
+          </div>
+          <button
+            type="button"
+            className="desktop-sidebar__logout"
+            onClick={onLogout}
+            title="Abmelden"
           >
-            {(user?.name || user?.email || '?').trim().slice(0, 1).toUpperCase()}
-          </div>
-          <div className="desktop-sidebar__user-text">
-            <span className="desktop-sidebar__user-name">
-              {user?.name || user?.email || 'User'}
-            </span>
-            {tier ? (
-              <span className="desktop-sidebar__user-tier">{tier}</span>
-            ) : null}
-          </div>
+            <LogOut size={18} />
+          </button>
         </div>
-        <button
-          type="button"
-          className="desktop-sidebar__logout"
-          onClick={onLogout}
-          title="Abmelden"
-        >
-          <LogOut size={18} />
-        </button>
       </div>
     </aside>
   )